The adverb really refers to something actual or genuine. If your ring is really pure gold, does that mean he really likes you?
Although the actual origin of really is unknown, it was first used in the 15th Century in the Eucharist, referring to the actual presence of Christ, and that definition holds today. Another use of the word, that of a questioning interjection ("Oh, really?"), was first recorded in 1815 and carries with it a sense of disbelief. Oh, really? You're late to work because the bus was attacked by a pack of wild boars? Do you really expect your boss to believe that?